A proton exchange membrane fuel cell (PEMFC) stack, which is widely used in automobiles and mobile phones, has a special structure in that a membrane and electrode assembly (MEA) is inserted in between a proton electrode and an oxygen electrode. This structure is repeated to eventually obtain a layered structure.
The number of separator plates and MEAs directly relates to the function of a fuel cell and it varies greatly depending on the output required. In particular, the PEMFC stack can have up to a few hundred of such structures. Therefore, the gasket that is installed two per each separator plate should be easily mounted so that the separator and MEA can be assembled efficiently. Further, it is desirable that the gasket be light-weight with low volume to maintain the pressure at the time of assembly to the minimum level. In addition, the gasket is required to be able to prevent impurities from entering the internal space of the stack while preventing the mutual introduction between a fuel gas and a coolant n the manifold.
In general, a PEMFC stack may comprise two separator plates having electric conductivity, where each of which comprises an oxygen electrode and a hydrogen electrode on either side, and an MEA, which generates electricity by passing protons through it. The PEMFC stack is assembled so that each of the separator plates is disposed on either side of the MEA and each gasket is disposed in between MEA and each separator plate. These members require relatively higher output compared to that of series structure and thus it is requested that the gasket be manufactured with least volume and surface pressure.
Considering that a few hundred of separator plates and MEAs are assembled in a series-layered structure there is required an efficient method for installation. Gaskets used in unit cell for fuel cell stack are sealed because they are disposed in between a separator plate and MEA, but the difference in the rate of expansion and shrinkage results in change in MEA and the gasket. This results from repetition of expansion and shrinkage due to heat generated by the contact between the rubber gasket and MEA, which experiences frequent expansion and shrinkage because of change in temperature and humidity. As the gasket and MEA experience repetitive expansion and shrinkage due to heat, there occurs a capillary phenomenon through which a coolant migrates and then reacts with hydrogen and oxygen thereby deteriorating or destroying the functions of the fuel cell. Further, the outer boundaries of the separator plate, MEA, and gasket are not completely aligned and thus interfere with the flow of a gas. This leads to uneven supply of the gas thereby deteriorating the functions of the fuel cell.
In the conventional gasket where the cross-section is provided with one row of beads, there is generated microspace due to the difference in the rate of expansion and shrinkage of the MEA and gasket by heat. The microspace causes the capillary phenomenon which makes the coolant in the manifold enter the region of chemical reaction in the fuel cell thus contaminating the MEA and drastically reducing the functions of the fuel cell. Further, when the gasket moves in the groove of the separator plate, the gasket which is in dual contact with both surfaces of the MEA is dislocated thereby lowering surface pressure and sealing property.
Therefore, the gasket used in the conventional unit cell for fuel cell stack has disadvantages that ethylene glycol, which is used for preventing the increase in operating temperature of the separator plate, penetrates the interior of separator plates and also it requires much time for assembly because of its poor mountability.